In tennis, the grunting phenomenon has been present for decades, but the idea that loud noise affects performance applies to other sports as well. In weight lifting the Valsalva maneuver, a forced suppression of breath during exhalation, has long been known to improve an athlete’s strength, and is often attended by a loud audible noise. In martial arts, a kiai is a sort of battle cry made during an attack to increase power, startle opponents, and maintain good breathing rhythm.

In the new tennis study, researchers found that grunting actually did increase ball velocity, to the tune of 3.8% faster speeds on average. At elite levels in sports, every percentage point counts, so this was a valuable contribution. The researchers reckoned it was enough to actually reduce the accuracy and power of the return shot.

Nevertheless, although ball velocity went up, it stands to reason there could have also been an associated detriment, such as increased heart rate. If the energy demands related to increased ball velocity became too great, it could make the athlete sluggish and unable to maintain the heightened pace, worsening performance overall. The researchers studied these potential costs of grunting as well. They looked at heart rate, VO2 max, and perceived exertion, and they found none of these factors significantly increased. So the average increase in ball velocity doesn’t require more total effort, just a loud sound.

One limitation of this study was that there may have been a placebo effect. In science, it’s a good idea to avoid the placebo effect when possible. This is done by “blinding” the participants to the key circumstances of the research. Unfortunately, there’s no way to create a blinded condition for grunting versus not. In other words, the tennis players in the study knew whether or not they were grunting, so it is possible that they simply exerted themselves harder when grunting because they believed it made them better.

Despite the inability to eliminate the influence of placebo, the fact remains that ball velocities increased without apparent cost. So long as you believe it works, according to this study, it will work. If you’ve been avoiding the grunt in your tennis matches, or in other sports, for that matter, it’s time to trade in bashfulness for heightened performance.